GB2502085A

GB2502085A - Carbon capture by metal catalysed hydration of carbon dioxide

Info

Publication number: GB2502085A
Application number: GB1208511.4A
Authority: GB
Inventors: Lidija Siller; Gaurav Ashok Bhaduri
Original assignee: University of Newcastle, The; Newcastle University of Upon Tyne
Current assignee: University of Newcastle, The; Newcastle University of Upon Tyne
Priority date: 2012-05-15
Filing date: 2012-05-15
Publication date: 2013-11-20
Also published as: SG11201407555YA; WO2013171480A2; US20150151248A1; EP2849871B1; JP2015523904A; CN104428051B; AU2013261615B2; ES2691198T3; GB201208511D0; AU2013261615A1; US9789439B2; CN104428051A; JP6367184B2; DK2849871T3; WO2013171480A3; EP2849871A2

Abstract

The use of a solid metal as a catalyst for the hydration of carbon dioxide, wherein the solid metal catalyst is selected from cobalt, nickel, copper, and zinc. Preferably, the solid metal is nickel. The solid metal may be in the form of particles, wires or fibres; or nanoparticles, nanowires, or nanofibres. The solid metal may be immobilized on a solid support, preferably an oxide. A method of capturing carbon dioxide comprises reacting carbon dioxide with water in the presence of solid metal catalyst as previously defined. A method of producing calcium carbonate comprises reacting carbon dioxide with water in the presence of a solid metal catalyst as previously defined, and adding a base and an M2+ solution to the product of the reaction between carbon dioxide and water where M is selected from calcium and magnesium or a mixture of the two. Apparatus for capturing carbon dioxide comprising a hydration tank containing a liquid comprising water and a solid metal as previously defined in contact with the liquid, and a means for bubbling carbon dioxide through the liquid. Also claimed is calcium carbonate containing detectable amounts of nickel particles.

Description

CARBON CAPTURE

[0001] This invention relates to methods and apparatus for the capture or fixation of carbon dioxide and to methods of increasing the rate of hydration of carbon dioxide. The methods use a solid metal to catalyse the hydration of carbon dioxide.

BACKGROUND

[0002] Carbon dioxide (C02) is released into the atmosphere by the burning of wood, coal, oil and gas. It can also be released by volcanoes and livestock. The pre-industrial carbon dioxide level was around 278 ppm and had stayed fairly constant for several centuries. In the 20th century atmospheric carbon dioxide levels have increased from about 315 ppm in 1958 to 378 ppm at the end of 2004. Thus, since the beginning of the industrial revolution the concentration of carbon dioxide in the atmosphere has increased by around 36%. Carbon dioxide is a greenhouse gas, contributing to the increasing of the temperature of the earth. Carbon dioxide from the atmosphere is also absorbed by the oceans where it forms carbonic acid and increases the acidity of the water, impacting on populations of many life forms and threatening delicate ecosystems such as the coral reefs.

[0003] One method of reducing the amount of carbon dioxide in the atmosphere is to capture and store it as it is produced rather than release it into the atmosphere.

[0004] Of the various approaches to the capture and storage of carbon dioxide, the one that has gained the interest of governments and industries is storage of carbon dioxide in geological forms. The geological storage of carbon dioxide can be achieved in two ways: a) separate the carbon dioxide and pump it into empty or depleted oil wells (both terrestrial and oceanic oil wells can be used); or b) to convert it into calcium carbonate and dispose of it as landfill. One limitation of method a) is that there has to be a continuous monitoring of the oil well for possible leaks (especially for oceanic storage). The conversion to calcium carbonate for use in landfill is considered to provide a more reliable solution to the problem of carbon dioxide storage.

[0005] Calcium carbonate is a thermodynamically stable material and is abundantly found on the earth's surface. The calcium carbonate present on the earth is estimated to be a carbon reservoir equivalent to 150,000 x 1012 metric tons of carbon dioxide.

Carbonates have been proven safe for long-term storage of carbon dioxide. An alternative to calcium carbonate is magnesium carbonate, which has similar properties. A combination of calcium and magnesium carbonate can also be used. The conversion of carbon dioxide into calcium carbonate (or other carbonates) is known as mineralisation. The rate limiting step in the mineralization of carbon dioxide is the hydration of carbon dioxide to form carbonate ions.

[0006] At present carbonic anhydrases (CAs) are seen as the most promising candidate for sequestering carbon dioxide. CAs catalyse the reversible hydration of carbon dioxide at mild pH values, with the fastest rates being observed for human CA II. The cost of extraction of enzymes limits their utility in the industrial context. They also only operate in a narrow pH range and so require the presence of a buffer. Additionally, enzymes can be unstable at elevated temperatures. There are some examples in the literature of carbonic anhydrase immobilised on nanoparticles being used for the hydration and capture of carbon dioxide (Vinoba etal., Langmuir, 2011, 27, 6227-6234; Vinoba etal., Journal of Molecular Catalysis B: Enzymatic, 75, 2012, 60-67). The nanoparticles were impregnated onto silica/alumina support.

[0007] Recently there have been a few reports on organometallic complexes being used for the reversible hydration of carbon dioxide. HoIm et al (!norg. Chem. 2011, 50, 100070- 81; Proc. Nat Acad. ScL, 2011, 108, 1222-7) have shown that nickel hydroxide complexes with 2,6-pyridinedicarboxamidate pincer ligands fix carbon dioxide very rapidly, but these processes are not catalytic. Organometallic compounds can be unstable to extreme conditions.

[0008] Accordingly, there remains a need for an improved method for the capture of carbon dioxide.

BRIEF SUMMARY OF THE DISCLOSURE

[0009] In a first aspect of the invention is provided the use of a solid metal as a catalyst for the hydration of carbon dioxide, wherein the solid metal is selected from Go, Ni, Cu and Zn.

[0010] In a second aspect of the invention is provided a method of capturing carbon dioxide; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Go, Ni, Cu and Zn.

[0011] In a third aspect of the invention is provided a method of increasing the rate of hydration of carbon dioxide; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Go, Ni, Cu and Zn.

[0012] In a fourth aspect of the invention is provided a method of reducing the amount of carbon dioxide which enters the atmosphere from combustion, the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Co, Ni, Cu and Zn.

[0013] In a fifth aspect of the invention is provided a method of producing calcium carbonate; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Co, Ni, Cu and Zn; and adding a base and a M2 solution to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca and Mg, or a mixture of the two.

[0014] In a sixth aspect of the invention is provided the use of a solid metal for capturing carbon dioxide, wherein the solid metal is selected from Co, Ni, Cu and Zn.

[0015] In a seventh aspect of the invention is provided an apparatus for carbon capture; the apparatus comprising: a hydration tank containing a liquid comprising water and a solid metal selected from Co, Ni, Cu and Zn in contact with the liquid; a means for bubbling CO2 through the liquid.

[0016] In an eighth aspect of the invention is provided a kit for capturing carbon dioxide, the kit comprising: a solid metal catalyst selected from Co, Ni, Cu and Zn; and instructions for use of the solid metal catalyst in capturing carbon dioxide; [0017] The following embodiments may apply, where appropriate, to any aspect of the invention.

[0018] In a preferred embodiment, the metal is Ni.

[0019] In an embodiment, the solid metal is in the form of particles, wires or fibres. The solid metal may be in the form of particles. The particles may be microparticles or nanoparticles. The metal may also be in the form of nanowires or nanofibres. In a preferred embodiment, the metal is in the form of nanoparticles, nanowires or nanofibres.

The metal may be in the form of nanoparticles.

[0020] The solid metal may also be in the form of foams and/or flakes, e.g. nanofoams and/or nanoflakes.

[0021] In a preferred embodiment, the solid metal is Ni nanoparticles, nanowires or nanofibres. In a particularly preferred embodiment, the solid metal is Ni nanoparticles.

[0022] In an embodiment, the solid metal is immobilised on a solid support. In an embodiment, the support is an oxide support, e.g. a silicate support or an alumina support.

[0023] In a ninth aspect of the invention is provided calcium carbonate containing a detectable amount of nickel particles.

[0024] In an embodiment, the nickel particles are nickel nanoparticles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows transmission electron microscopy images of Ni nanoparticles.

Figure 2 shows Energy Dispersive X-ray Spectroscopic results of Ni nanoparticles.

Figure 3 shows Selected Area Electron Diffraction result of Ni nanoparticles.

Figure 4 shows Increase in the amount of carbon dioxide absorbed in aqueous solution of Ni nanoparticles as a function of particle concentration.

Figure 5 shows pH change and conductivity change when carbon dioxide is bubbled in DI water and aqueous Ni nanoparticle suspension a) starting from pH above 6; b) starting at pH value below 6.

Figure 6 shows pH change as CO2 and argon are sequentially bubbled through a suspension of nickel nanoparticles.

Figure 7 shows a schematic diagram of an apparatus suitable for practicing the methods of the invention.

DETAILED DESCRIPTION

[0026] When bubbled through water carbon dioxide is hydrated to form carbonic acid, carbonate ions and/or bicarbonate ions depending on the conditions employed. Unless a buffer or a base is present in the solution, a carbonic acid solution is generated. The inventors have surprisingly identified that solid transition metals can be used as catalysts to increase the rate at which the carbon dioxide is converted to carbonic acid, carbonate ions and/or bicarbonate ions. In other words, the inventors have surprisingly identified that solid transition metals can catalyse the hydration of carbon dioxide. The solid metal may also increase the amount of carbon dioxide which can be fixed by the solution.

[0027] Advantageously, the use of a solid metal, rather than a metal ion encapsulated in an enzyme or complexed with organic ligands, allows the carbon capture process to be conducted under a wider range of conditions! e.g. high temperatures, high pressures, low pressures, high pH, low pH. At higher temperatures, enzymes and organometallic complexes are prone to decomposition and this can limit their utility, especially when capturing 002 from a combustion process which necessarily also produces heat.

Enzymes and many organometallic complexes are only stable in relatively narrow pH ranges.

[0028] A further benefit of the use of a solid metal is that a solid metal can be more easily retrieved (e.g. by filtration, sedimentation, centrifugation) from the hydration reaction mixture than species which are soluble in water. Once recovered from the reaction a solid metal can be reused.

[0029] A solid metal can be used as a catalyst for the hydration of carbon dioxide on an industrial scale.

[0030] By solid metal is meant a solid which comprises the metal. A solid metal may be a metal which is substantially present in the (0) oxidation state. It may be, for example, that the majority of the metal is in the (0) oxidation state. As an example, if the metal is nickel the majority of the nickel may be present as Ni(0). It is possible that the metal is also present in other oxidation states. It is possible that the active form (i.e. the catalytic form) of the metal is not the (0) oxidation state. For example, in the case of nickel, it may be that positive nickel ions (e.g. Ni2 ions) on the surface of the metal are the active catalytic species. It is equally possible that the (0) oxidation state of the metal (e.g. nickel(0)) is the active catalytic species.

[0031] It is within the scope of this invention that the solid metal comprises other elements. Thus, the solid metal may substantially be a solid compound which contains the metal and which is not soluble in the medium of the reaction, e.g. which is not soluble in water. Thus, in the case of nickel, the solid metal may substantially be a solid Ni2 compound which is not soluble in water, e.g. NiO. Alternatively, the solid metal may substantially be a compound in which nickel is in any other positive oxidation state, e.g. Ni02 or Ni203. As an illustrative example, if the solid metal is nickel nanoparticles, this includes both Ni nanoparticles and NiO nanoparticles.

[0032] The metal may comprise other materials. It may be in the form of a thin film on a substrate comprising the other materials. Such a thin film may be formed by any means known to those in the art, e.g. vapour deposition, plasma deposition, electroplating etc. The thin film may be a layer of a laminate, preferably being one of the outer layers of that laminate. The other materials may be other metals (e.g. other transition metals).

Alternatively, the solid metal may be in the form of an alloy comprising the metal. In embodiments in which the metal is in the form of a nanoparticle, the nanoparticle may be immobilised on a support.

[0033] Although the aspects of the invention specifically described in the present application are directed to solid metals selected from Co, Ni, Cu or Zn, it is within the scope of the invention that the solid metal is any transition metal.

[0034] Transition metal' refers to any element in the transition period (i.e. the d-block) of the periodic table. Thus, transition metal may refer to one or more elements selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg.

[0035] In a preferred embodiment of the reaction the solid metal is nickel. Nickel is ferromagnetic. A ferromagnetic metal allows the easy separation of the metal from a reaction mixture using some form of magnet. If necessary, it also allows the easy separation of the metal from other solid products of the reaction, again using some form of magnet e.g. using magnetic field filtration. This eases the recovery of the metal and allows it to be reused, thus reducing costs.

[0036] In some embodiments of the invention the solid metal is in the form of particles, such as nanoparticles and microparticles, nanowires or nanofibres. Smaller solid metal forms, such as micro-and nano-particles, nanowires or nanofibres offer the benefit of a substantially increased surface area compared to the same quantity of larger pieces of metal, increasing the amount of metal atoms which are available for performing the catalysis.

[0037] Nanoparticles will be readily understood by those skilled in the art as referring to particles in which the majority of the particles are 100 nm or less in size.

[0038] Microparticles will be readily understood by those skilled in the art as referring to particles in which the majority of the particles are from 0.1 to 100 pm in size.

[0039] Nanowires and nanofibres are wires and fibres with a diameter which is 100 nm or less.

[0040] Capturing carbon dioxide can be understood to mean the conversion of carbon dioxide gas into a form which can be easily transported and stored, i.e. conversion to a safe and stable solid or liquid.

[0041] The carbon dioxide which is captured or hydrated in the methods of the invention may have been released by combustion. It may have been released by livestock. It may have been released by a volcano.

[0042] The carbon dioxide may be the direct product of the process in which it was generated or it may have been purified or partially purified prior to being captured in the method or use of the invention. It may contain other products of the process in which it was generated such as carbon monoxide, sulphur dioxide, hydrogen sulphide, methane, other organic molecules, particulate matter, steam, nitrogen oxides. Alternatively, the carbon dioxide may be substantially pure.

Methods of the Invention The invention provides a method of capturing carbon dioxide, increasing the rate of hydration of carbon dioxide, or reducing the amount of carbon dioxide which enters the atmosphere from combustion; the method comprising reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Co, Ni, Cu and Zn.

[0043] In an embodiment, the method further comprises the step of separating the solid metal from the product of the reaction between carbon dioxide and water.

[0044] In an embodiment, the method further comprises the step of adding a M24 solution to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca or Mg, or a mixture of the two.

[0045] In an embodiment, the method further comprises the step of adding a base to the product of the reaction between carbon dioxide and water.

[004.6] In an embodiment, the method further comprises the step of adding a M2 solution and a base to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca or Mg, or a mixture of the two.

[0047] In an embodiment, the M2 solution is an MCI2 solution. In an embodiment, the M2 solution is a Ca2 solution. In a preferred embodiment, the M24 solution is a CaCI2 solution.

[0048] In an embodiment, the base comprises hydroxide ions. In a further embodiment, the base is an alkali metal hydroxide (e.g., LiOH, NaOH or KOH). In a preferred embodiment, the base is NaOH.

[0049] In an embodiment, the base is in solution, e.g. an aqueous solution. In a further embodiment, the concentration of the base is 1 M or less. In a preferred embodiment, the concentration of the base is from 0.1 M to 0.5 M. [0050] In an embodiment, reacting carbon dioxide with water comprises passing carbon dioxide through a liquid! wherein the liquid comprises water.

[0051] Passing carbon dioxide through' may mean bubbling carbon dioxide through'.

Bubbling' will be readily understood by the person skilled in the art to mean delivering a gas into a liquid at a point below the surface of that liquid, and allowing the gas to move upwards through the liquid.

[0052] In an embodiment, the liquid is water or an aqueous solution.

[0053] In an embodiment, the solid metal (e.g. nickel) is suspended in the liquid.

[0054] In an embodiment, the reaction between carbon dioxide and water is performed at a temperature of 25 °C or above. In an embodiment, the temperature may be from 25 to °C. In an embodiment, the temperature is from 50 to 70 °C. It may be that the CO2 is at a temperature greater than 25 °C before it is passed through the liquid.

[0055] In an embodiment, the reaction of carbon dioxide with water occurs in a hydration tank.

[0056] The word tank' used in this specification (for instance hydration tank' or settling tank:) is not intended to be limiting. A tank' may be any vessel suitable for holding a liquid.

For example, a tank' may be sealed or it may be open.

[0057] In an embodiment, the solid metal (e.g. nickel) may be sonicated prior to use.

This sonication can occur before the metal is added to the hydration tank or while the metal is in the hydration tank.

[0058] In an embodiment, the solid metal (e.g. nickel) is mixed with the water prior to addition to the hydration tank. This may occur in a mixing chamber.

[0059] In an embodiment, the liquid may be heated in the hydration tank. It may be that the CO2 is at a temperature greater than 25 °C before it is passed through the liquid. In an alternative embodiment, the CO2 may be cooled before being passed through the liquid.

[0060] In an embodiment, the CO2 may be purified or partially purified before being passed through the liquid.

[0061] Partially purified' can be understood to mean that one or more substances (e.g. other gases) which were mixed with the carbon dioxide have been removed. These other substances may be completely removed or they may be partially removed. This removal can be achieved using filters or scrubbers or other means which would be readily understood by those in the art.

[0062] In an embodiment, the concentration of the solid metal in the liquid is greater than about 10 ppm. In a further embodiment, the concentration is from about 10 to about 100 ppm. In an embodiment, the concentration is from about 10 to about 50 ppm. In an embodiment, the concentration of the solid metal in the liquid is about 30 ppm.

[0063] In an embodiment, the method further comprises the step of adding a solution comprising M2 ions to the liquid after the CO2 has been passed through the liquid, wherein M is selected from Ca or Mg, or a mixture of the two.

[0064] In an embodiment, the CO2 is passed through the liquid in a hydration tank, the liquid is transferred to a settling tank, and the M2 solution is added to the liquid in the settling tank, wherein M is selected from Ca or Mg, or a mixture of the two. Alternatively, the CO2 is passed through the liquid and the M2 solution is added to the liquid in the same tank.

[0065] In an embodiment, the method further comprises the step of adding a base to the liquid after the CO2 has been passed through the liquid. In an embodiment, the CO2 is passed through the liquid in a hydration tank, the liquid is transferred to a settling tank, and the base is added to the liquid in the settling tank. Alternatively, the CO2 is passed through the liquid and the base is added to the liquid in the same tank.

[0066] In an embodiment, the method further comprises the step of adding a M24 solution and a base to the liquid after the CO2 has been passed through the liquid, wherein M is selected from Ca or Mg, or a mixture of the two. In an embodiment, the CO2 is bubbled through the liquid in a hydration tank, the liquid is transferred to a settling tank, and the M2 solution and the base are added to the liquid in the settling tank. Alternatively, the CO2 is passed through the liquid and the Ca2 solution and the base are added to the liquid in the same tank.

[0067] The M2 solution may also comprise the base or it may be added separately to the base.

[0068] In an embodiment, the pH of the liquid in the sealing tank is maintained at a level greater than about 5. In a further embodiment! the pH of the liquid in the settling tank is maintained at a level from about 6.5 to about 7. The maintenance of the pH can be achieved by controlling the rate of addition of the liquid from the hydration tank or by controlling the rate of addition of the base.

[0069] In an embodiment, the M2 solution is an MCI2 solution. In an embodiment, the M2 solution is a Ca2 solution. In a preferred embodiment, the M2 solution is a CaCI2 solution.

[0070] In an embodiment, as the liquid is transferred to the settling tank it passes through a separator which separates the solid metal from the liquid. If the metal is ferromagnetic (e.g. if the metal is nickel), the separator may be a magnetic separator.

[0071] In an alternative embodiment, the liquid is separated from the solid metal before the liquid is transferred from the hydration tank. This may be achieved by filtration, particularly if the metal is attached to a solid support. In this embodiment, the solid metal may remain in the hydration tank. In embodiments in which the metal is ferromagnetic, a magnet may be used to retain the metal in the hydration tank.

[0072] In an embodiment, once separated from the liquid, the metal is transferred to the hydration tank. It may be transferred directly or it may be mixed with water and then added to the hydration tank. Thus it may be transferred to a mixing chamber, mixed with water and then transferred to the hydration chamber.

[0073] In embodiments in which the liquid in the hydration tank is heated, it may be cooled before it is added to the settling tank.

[0074] In an embodiment, the method further comprises the step of separating a solid product from the liquid. Solid product' may be understood to mean a solid product which is formed at any stage of the method described herein. The solid product may be formed during the hydration step or it may be formed during subsequent steps, such as when a M2 solution is added to the product of the reaction between carbon dioxide and water.

[0075] In some embodiments, this solid product will comprise MCO3 and the separation will occur after the M2 solution has been added to the liquid. In a preferred embodiment, the settling tank is attached to a solid separator.

[0076] It may be that the solid product also comprises the solid metal. In other words the solid which is separated from the liquid contains both the solid metal and a solid product which is formed at any stage of the method of the invention. In an embodiment, the method further comprises the step of separating the solid metal from the solid product. If the metal is ferromagnetic (e.g. if the metal is nickel), this may be achieved using a magnet. In an embodiment, once separated from the solid product, the metal is transferred to the hydration tank.

[0077] In some embodiments the isolated solid product may contain detectable amounts of the solid metal.

[0078] In an embodiment, the method further comprises removing excess liquid from one or both of the tanks. In an embodiment, the method further comprises removing excess liquid from the settling tank. This excess liquid may be an alkali metal chloride solution (e.g. a sodium chloride solution).

[0079] In an embodiment! the methods of the invention are continuous.

Apparatus of the invention [0080] In a seventh aspect of the invention is provided an apparatus for carbon capture; the apparatus comprising: a hydration tank containing a liquid comprising water and a solid metal selected from Co, Ni, Cu and Zn in contact with the liquid; a means for bubbling CO2 through the liquid.

[0081] In an embodiment, the apparatus further comprises: a sealing tank connected to the hydration tank and a means for transferring the liquid from the hydration tank to the sealing tank.

[0082] In an embodiment, the apparatus further comprises a mixing chamber attached to the hydration tank. In an embodiment, the mixing chamber comprises a mixing device, e.g. a mechanical stirrer.

[0083] In an embodiment, the apparatus comprises a means for separating the solid metal from the liquid. In an embodiment, this means is situated in the hydration tank. In an alternative embodiment, the means for transferring the liquid from the hydration tank to the settling tank comprises a means for separating the solid metal from the liquid. In an embodiment, the means is a means of filtering. In an embodiment, the means is a magnetic means.

[0084] In an embodiment, the means for transferring the liquid from the hydration tank to the settling tank comprises a cooling device.

[0085] In an embodiment, the hydration tank comprises a vent.

[0086] In an embodiment, the hydration tank comprises a source of water.

[0087] In an embodiment, the hydration tank comprises a heat source.

[0088] In an embodiment, the sealing tank comprises a source of Ca2.

[0089] In an embodiment, the settling tank comprises a source of base (e.g. a source of hydroxide ions).

[0090] In an embodiment, the settling tank comprises a mixing device, e.g. a mechanical stirrer.

[0091] In an embodiment, the hydration tank comprises a mixing device, e.g. a mechanical stirrer.

[0092] In an embodiment, the settling tank comprises one or more outlet pipes. These outlets are preferably situated towards the top of the settling tank.

[0093] In an embodiment, the apparatus comprises a means for separating solid product from a liquid. In an embodiment, this means is attached to the settling tank. In an embodiment! this means is preferably attached at or near the bottom of the settling tank.

In an embodiment, this means is a screw conveyor.

[0094] In an embodiment, the apparatus is suitable for carrying out the methods of the invention.

[0095] Figure 7 shows a schematic diagram of an apparatus suitable for practicing the methods of the invention. This is provided for illustrative purposes only and is not intended to limit the scope of the invention.

[0096] The apparatus comprises a hydration tank 1 and a settling tank 2.

[0097] The hydration tank comprises a bubbler 3 (which may also be known as a sparger) which allows the gas containing CO2 to be bubbled through the hydration tank 1.

The hydration tank also comprises a vent 4 situated towards the top of the hydration tank, through which any CO2 free gas can escape. In use the hydration tank will contain water and nickel nanoparticles and the CO2 gas which is bubbled through the tank will be converted to carbonic acid in solution.

[0098] The apparatus also comprises a mixer chamber 6 in which the nickel nanoparticles are suspended in water. The mixer chamber 6 comprises a mechanical stirrer 7 and a motor 8, which drives the stirrer 7.

[0099] The carbonic acid solution, with the nickel nanoparticles in suspension is connected to a magnetic separator 5. This separates the ferromagnetic nickel nanoparticles from the carbonic acid solution. The nickel nanoparticles are then transferred back to into the mixer chamber 6 and reused in the hydration reaction. The carbonic acid solution is transferred to the settling tank 2.

[00100] A NaOH solution and a CaCI2 solution are added to the settling tank 2 and solid calcium carbonate is formed, along with NaCI is solution.

[00101] The settling tank 2 comprises a mechanical stirrer 9, driven by a motor 11.

[00102] The settling tank 2 comprises one or more outlet pipes 10 through which excess liquid, which largely comprises an NaCI solution, flows. The settling tank is connected, towards the bottom, to a screw conveyor 13 which continuously removes the solid CaCO3 from the settling tank. The screw conveyor is driven by a motor 12.

[00103] Throughout the description and claims of this specification, the words comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00104] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[00105] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Examples -General Experimental [00106] CO2 cylinder (99% pure) was bought from BOC. The nickel nanoparticles were purchased from Nano Technologies, Korea. Sodium hydroxide and hydrochloric acid (0.1 M) were bought from Sigma Aldrich and were used without further purification. The water used both for the examples and for chemical preparation was distilled and filtered and had a low conductivity. 0.1 M NaOH solution was prepared by dissolving NaOH in deionised water and was standardised using 0.1 M HCI solution.

Example I

[00107] The purchased nanoparticles were characterized using transmission electron microscopy (TEM) to determine the size distribution of the nanoparticles. The TEM images of the Ni nanoparticles can be seen in Figure 1. The size of majority of the particles was below 100 nm as prescribed by the manufacturer. The presence of the Ni nanoparticles was confirmed using energy dispersive X-ray spectroscopy (EDX) seen in Figure 2. The crystal planes of the nanoparticles can be seen by the Selected Area Electron Diffraction (SAED) pattern (Figure 3) and correspond to the [222], [311], [222], [400], [422] and [531] lattice planes respectively. From the pattern it can be concluded that the nanoparticles are poly crystalline in structure.

Example 2

[00108] The experiment for determination of concentration of CO2 was done in a 20 ml jacketed vessel purchased from Soham Scientific. CO2 gas (at 1 atm) was bubbled in 10 ml of deionised water or Ni nanoparticle suspension for 30 mm and then titrated with 0.1 M NaOH solution.

[00109] It is observed that when Ni nanoparticles are present in water, the carbon dioxide content of the solution after 30 mm of bubbling increases (Figure 4). As the concentration of nickel nanoparticles is increased there is an observed increase in the amount of carbon dioxide present in the water until a maximum is reached (at 30 ppm) and then the value slowly decreases.

Example 3

[00110] The CO2 absorption rate experiments were done in a kit consisting of a fixed volume (200 ml) of water and CO2 was sparged at 1 atm (0.01 MPa) pressure using a sinter. The pH and conductivity was measured a pH 209 bench top pH meter (Hanna Instruments) and plONneer3O (Radiometer analytical). The temperature was maintained using a temperature bath BS5 (Fisher Scientific). The concentration of nickel nanoparticles was 30 ppm.

[00111] The rate of change of pH and conductivity can be seen in Figures 5a and Sb. Two sets of experiments were performed at different pH values to test the catalytic activity of Ni nanoparticles at pH values above and below 6 (Fig. 5a and Fig. 5b respectively). Since a drop in pH occurs due to the formation of carbonic acid, the rate of change in pH is related to the rate of reaction (rA). It can be seen from figures 5a and 5b that, in both cases, the rate of change in pH in the presence of the catalyst is faster than the rate of change in pH in the absence of the catalyst.

[00112] Likewise, it can be observed from Figures 5a and 5b that the rate of increase in the conductivity of the solution is higher in the presence of the nanoparticles than without.

Example 4

The nanoparticles were suspended in water and subjected to sonication for five minutes.

The suspension was then bubbled with CO2 gas (absorption run, seen by the drop of pH) for 30 mm at one atmosphere pressure. Then the gas was changed to argon (desorption run, seen by increase in pH), and bubbled for another 30 mm. At the end of the 25 mm (desorption) the suspension was again sonicated and the procedure repeated again. The pH was continuously monitored for the absorption and desorption run and the variation in pH can be seen in Figure 6.

Claims

CLAIMS1. A use of a solid metal as a catalyst for the hydration of carbon dioxide, wherein the solid metal is selected from Co, Ni, Cu and Zn.
2. The use of claim 1 or claim 2, wherein the solid metal is Ni.
3. The use of any preceding claim, wherein the solid metal is in the form of particles, wires or fibres.
4. The use of claim 3, wherein the solid metal is in the form of nanoparticles, nanowires or nanofibres.
5. The use of claim 4, wherein the solid metal is in the form of nanoparticles.
6. The use of any one preceding claim, wherein the solid metal is immobilised on a solid support.
7. The use of claim 6, wherein the support is an oxide support.
8. A method of capturing carbon dioxide; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Go, Ni, Cu and Zn.
9. A method of increasing the rate of hydration of carbon dioxide; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Go, Ni, Cu and Zn.
10. The method of claim 8 or claim 9, wherein the solid metal is Ni.
11. The method of any one of claims 8 to 10, wherein the solid metal is in the form of particles, wires or fibres.
12. The method of claim 11, wherein the solid metal is in the form of nanoparticles, nanofibres or nanowires.
13. The method of claim 12, wherein the solid metal is in the form of nanoparticles.
14. The method of any one of claims 8to 13, wherein the solid metal is immobilised on a solid support.
15. The method of any one of claims 8 to 14, wherein reacting carbon dioxide with water comprises passing carbon dioxide through a liquid, wherein the liquid comprises water.
16. The method of claim 15, wherein the liquid is water or an aqueous solution.
17. The method of claim 15 or claim 16, wherein the solid metal is suspended in the liquid.
18. The method of any one of claims 8 to 17, wherein the method further comprises the step of adding a M2 solution to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca and Mg, or a mixture of the two.
19. The method of any one of claims 8 to 18, wherein the method further comprises the step of adding a base to the product of the reaction between carbon dioxide and water.
20. The method of any one of claims 8 to 17, wherein the method further comprises the step of adding a M2 solution and a base to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca and Mg, or a mixture of the two.
21. The method of claim 18 or claim 20, wherein the M2 solution is an MCI2 solution.
22. The method of claim 19 or claim 20, wherein the base is an alkali metal hydroxide
23. The method of claim 22, wherein the base is NaOH.
24. The method of any one of claims 8 to 23, the method further comprising the step of separating the solid metal from the product of the reaction between carbon dioxide and water.
25. The method of any one of claims 8 to 24, wherein the method is continuous.
26. A method of reducing the amount of carbon dioxide which enters the atmosphere from combustion, the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Co, Ni, Cu and Zn.
27. A method of producing calcium carbonate; the method comprising: reacting carbon dioxide with water in the presence of a solid metal catalyst selected from Co, Ni, Cu and Zn; and adding a base and a M2 solution to the product of the reaction between carbon dioxide and water, wherein M is selected from Ca and Mg, or a mixture of the two.
28. A use of a solid metal for capturing carbon dioxide, wherein the solid metal is selected from Co, Ni, Cu and Zn.
29. An apparatus for capturing carbon dioxide, the apparatus comprising: a hydration tank containing a liquid comprising water and a solid metal selected from Co, Ni, Cu and Zn in contact with the liquid; a means for bubbling CO2 through the liquid.
30. A kit for capturing carbon dioxide, the kit comprising: a solid metal catalyst selected from Co. Ni, Cu and Zn; and instructions for use of the solid metal catalyst in capturing carbon dioxide;
31. Calcium carbonate containing a detectable amount of nickel particles.
32. The calcium carbonate of claim 31, wherein the nickel particles are nickel nanoparticles.
33. A use of a solid metal as a catalyst for the hydration of carbon dioxide, substantially as described herein with reference to the accompanying drawings.
34. A method of increasing the rate of hydration of carbon dioxide, substantially as described herein with reference to the accompanying drawings.
35. A method of capturing carbon dioxide, substantially as described herein with reference to the accompanying drawings.
36. An apparatus for capturing carbon dioxide, substantially as described herein with reference to the accompanying drawings.